Aluminum (Al) is ubiquitous in soils and at pH values below 5.0, is solubilized into the soil solution as the highly phytotoxic Al3+ species, which inhibits root growth and damages root systems (Kochian, 1995, Annu. Rev. Plant Biol. 46: 237-260). As such, aluminum toxicity is aggravated by acid precipitation (e.g., acid rain). For example, contaminated soils in Brazil contain aluminum in amounts that range from 11 to 124 g/Kg of soil. Another constraint on acid soils is phosphorous (P) deficiency, which is caused by P fixation with Al and Fe oxides on the surface of clay minerals in acid soils. See Sanchez et al. 1997. In: Replenishing Soil Fertility in Africa, ed. R Buresh, P Sanchez, F Calhoun, pp. 1-46). Root damage reduces water and nutrient uptake and thus crop productivity. Low soil pH has been documented to reduce the yield on nearly 25% of the world's land presently under production. See, Wood, et al. (2000) in Pilot Analysis of Global Ecosystems: Agroecosystems (Int. Food Policy Res, Inst. And World Resources Inst., Washington, D.C.), pp 45-54). Thus, there is a need to provide methods and materials for increasing aluminum tolerance in plants.